The present invention relates to a wireless communication system in which a mobile station relays a wireless signal sent from a base station to other mobile stations using a weak radio wave, more particularly to a method for transferring a wireless signal among the mobile stations in this wireless communication system.
The following is disclosed in Japanese Published Unexamined Patent Application No. Hei 9-252277. Referring to FIG. 1. Information transmitted from the fixed station (101) is first received by the mobile station A (103) and the information is processed by the station A. Then, the information is relayed to the mobile station B (105). Thereafter, the information is sequentially relayed to the mobile stations C (107) and D (109) from the mobile station B (105). In such manner, it becomes possible to transmit the information in a wide area with a small power by relaying the information. Moreover, the value of a re-transmitting counter is included in a transmitting frame, and the value of the re-transmitting counter is incremented by one after every relay. It is determined, according to the value of the re-transmitting counter whether the information is to be relayed or not. The present invention depicts that the information can be localized by implementing this method. However, a problem may be created if the information to be relayed is determined based on the number of relays. For example, if the relay is performed among the mobile stations located at short distances or close to one another, a problem arises that the limitation to the number of relays is reached before the information has propagated far from the fixed station.
The following is also disclosed in Japanese Published Unexamined Patent Application No. Hei 10-32538. Referring to FIG. 2. The mobile object CR1 collects data as to the present position and time from the GPS (Global Positioning System) apparatus GP1 during its running, and based on the data the running locus (course of travel) until the present time, the average speed, the elapsed time, the degree of the traffic congestion and the like on the course are stored in the memory MM1 as traffic information message MS1. Moreover, there is the following description relating to FIG. 3. xe2x80x9cIt is assumed that the mobile object CR1 and the mobile object CR2 become proximate with one another so that they are capable of communicating with each other. The mobile object CR2 sends the traffic information message MS2-2 stored therein to the mobile object CR1, and the mobile object CR1 sends to the mobile object CR2 the traffic information messages MS1 which is being possessed by the mobile object CR1 and the mail information message MS6 addressed to the computer, which is to be transmitted. In the traffic information message MS1 received by the mobile object CR2 important parts for the mobile object CR2 are displayed on the display device DS2 as newly-received information. Similarly, in the traffic information message MS2-2 received by the mobile object CR1, important parts for the mobile object CR1 are displayed on the display device DS1 as newly-received information. Although the message transfer system of this embodiment possesses no guarantee for data arrival, essentially, the arrival rate must be increased as high as possible. Since there are actually many mobile objects running in the same area, traffic information data concerning a certain area/route will be sequentially updated to the latest data. Particularly, in the case where traffic snarls occur as in Japan, other mobile objects are always present around a certain mobile object, it will be possible to exchange messages with substantially the same high speed and in the same wide range as those in a wired network. Moreover, there is a description in which since instant messages need not be transmitted in a wide range, the messages are not stored for a long time and are soon deleted. However, the prior art contains no description in which it is judged how instant the messages are and at what time the messages should be deleted. Furthermore, there is no description as to a problem if many mobile stations are mal-distributed.
In the background arts described above, the mechanism in which the information transmitted from either the base station or the fixed station is exchanged among the mobile stations is disclosed. However, only the fact that the processing in the mobile stations to control the propagation of the information is performed by the number of relays is disclosed. Accordingly, the object of the present invention is to provide a method for controlling the propagation of information in a more reasonable style.
Another object of the present invention is to limit the propagation of the information to a predetermined range.
Still another object of the present invention is to avoid congestion of the information to be propagated.
Still a further object of the present invention is to enable the information to be propagated more efficiently.
The system that is the premise in the present invention is analogous to the foregoing background arts. Specifically, the information sent by the base station (the fixed station in FIG. 1) as shown in FIG. 1 is transmitted, for example, from the mobile station A to the mobile station B, from the mobile station B to the mobile station C, sequentially, whereby the information propagates from the mobile station A to the mobile station C. As shown in FIG. 2, each mobile station has at least the antenna AT1, the display device DS1, the receiver RX1, and the transmitter TX1, and receives wireless signals by the receiver RX1 via the antenna AT1 and presents the information necessary for the user of this mobile station among the received wireless signals to the user with the display device DS1. On the other hand, the mobile station transmits the wireless signal including specific information to other mobile stations from the transmitter TX1 using the antenna AT1. As shown in FIG. 3, when the mobile station CR2 communicates with the mobile station CR1, the mobile station CR2 sends the received information MS2-2 to the mobile station CR1, and the mobile station CR1 sends the stored information MS1 and MS6 to the mobile station CR2. Thus, the information is exchanged between the mobile stations CR1 and CR2.
As understood from the above descriptions, although the exchanges of the information among the mobile stations are performed similarly to the background arts, the present invention shows which information is propagated among the mobile stations. Specifically, in a mobile wireless transceiver, if it is determined that received information including position information of an information origin transmitting information initially is to be transferred, the following steps are executed: calculating a distance from the information origin using the position information; comparing the distance with a predetermined threshold; and determining that the received information is not to be transferred if the distance is greater than or equal to the predetermined threshold. Thus, the propagation of the information is limited to a specific area from the information origin, so that it is possible to transmit more localized information to users in a specific area.
As another aspect of the present invention, in a mobile wireless transceiver, if it is determined that received information is to be transferred, the following steps are executed: judging whether a valid period of receiving information has expired; and determining that the received information is not to be transferred if the valid period thereof has expired. Obsolete information shall not be transferred, so that an overflow of the transferred information can be prevented. Moreover, if the velocity of the mobile station is approximately constant, the propagation area of the information will be limited to a specific area remote from the information origin. In the background arts, the fact is recited, in which the instant information is not stored for a long period of time, and it is deleted. However, there is no description concretely reciting on how to judge whether the message is instant and at what time the instant message is deleted.
If the received information includes a transmitting time information of the information original initially transmitting the information, the step of judging whether a valid period of the received information is expired or not includes a step of judging by using the transmitting time information, whether a predetermined time has passed from a transmitting time. If the received information includes information concerning a valid period time by the information origin initially transmitting the information, the step of judging whether a valid period of the received information is expired or not includes a step of judging whether the present time has passed the valid period time.
As still another aspect of the present invention, in a mobile wireless transceiver, if it is determined that a received information includes position information of a transmission source to be transferred, the following steps are executed: detecting a density of the mobile wireless transceivers in the vicinity; calculating a distance from the transmission source by using the position information of the transmission source; judging whether the density and the distance satisfy a specific condition; and determining that the received information is not to be transferred if the density and the distance satisfy the specific condition. Thus, if the density of the mobile stations is high, the information from the mobile station located at a short distance from itself is not re-transmitted, whereby an overflow of transmitted information can be controlled, resulting in a more efficient information transfer.
It is conceived that the step of judging whether a density of the mobile stations and a distance from the transmission source satisfy a predetermined condition may include a step of judging whether the density is a specific value or more and the distance is a specific value or less. It is also conceived that the step of judging whether the density and the distance satisfy the predetermined condition may include a step of determining whether the density and the distance satisfy a predetermined relationship. Note that the formula for the predetermined relationship expresses that the re-transmission is not performed in the case where the density of the mobile stations are high and the information from the mobile station is received a short distance from the mobile station.
As still another aspect of the present invention, in a mobile wireless transceiver, if it is determined whether or not received information including position information of an information origin initially transmitting information as well as position information of a transmission source is to be transferred, the following steps are executed: judging whether an angle formed by a straight line connecting the information origin and the transmission source and a straight line connecting the transmission source and the transceiver itself is within a specific value, by using on the position information of the information origin and of the transmission source; and determining that the received information is not to be transferred, if the transceiver itself is not within the specific value of the angle. Thus, it becomes possible to propagate the information to a remote place more efficiently, thus preventing an overflow of information which is transferred in a narrow area.
It may be conceived that the specified value of the angle is determined depending on the density of the mobile wireless transceivers.
As still another aspect of the present invention, in a mobile wireless transceiver, if it is determined that received information including position information of an information origin initially transmitting information as well as position information of a transmission source is to be transferred, the following steps are executed: detecting an average distance from other transceivers; judging whether the transceiver itself is within an area surrounded by two straight lines which make contact with a circle, by using the position information of the information origin and the position information of the transmission source, the center of which is located at a position apart from the transmission source by a receiving limitation distance as well as on a straight line connecting the information origin and the transmission source, and the radius of which is equal to the average distance; and determining that the received information is not to be transferred if the transceiver itself is not with the area. Thus, it becomes possible to propagate the information to a remote place more efficiently, thus preventing a flood of the information which is transferred in a narrow area.
It can be also conceived that in this aspect, the following steps are further executed: judging whether a distance from the transmission source is equal to or longer than a value obtained by subtracting the average distance from the receiving limitation distance; and determining that the received information is not to be transferred if the distance from the transmission source is shorter than the value obtained by subtracting the average distance from the receiving limitation distance.
The above description of the present invention was made for processing in the mobile station. The present invention can be also implemented for a mobile wireless transceiver which executes such processing. Moreover, the present invention can be implemented for a program which executes such processing. Noted that the program is usually stored in memory devices such as a ROM (Read Only Memory) and storage mediums such as a CD-ROM.